1. Field of the Invention
This invention is in the field of compressors of gases and vapors and particularly such compressors for use at several different pressures.
2. Description of the Prior Art
Prior art gas and vapor compressor systems, used to deliver several different discharge pressures, have used a separate compressor for each discharge pressure. For example, a factory using air motor driven tools together with pneumatic actuators or work positioners will usually prefer medium discharge pressures for the air motors and high discharge pressures for the actuators and positioners and two or more separate compressors would be required with prior art methods. When prior art gas and vapor compressor systems are used to pump from several different suction pressures, a separate compressor is used for each suction pressure. For example, a vapor compression refrigeration plant used to maintain several different temperatures, and hence refrigerant pressures, in several different food storage rooms will require a separate compressor for each different suction pressure and temperature. These prior art multicompressor gas and vapor compressor systems are thus costly since the individual compressors are one of the most expensive components in the system.
In some prior art gas and vapor compressor systems, all fluid is compressed by a single compressor to the highest working discharge pressure and then portions are throttled to lower working pressures to yield several different discharge pressures. Alternatively, where several different suction pressures are used, all gas and vapor can be throttled to the lowest suction pressure used and then all gas and vapor are pumped from this lowest suction pressure by a single compressor. But these prior art throttling methods for utilizing a single compressor to work at several different pressures suffer the disadvantage of requiring a greater power input to the compressor and thus an increased energy consumption and operating cost.
Where a single very high discharge pressure is used with a single low suction pressure, a single multistage compressor is commonly used in the prior art. These multistage compressors are also costly as requiring a separate piston and cylinder or rotor for each stage and can be considered as equivalent to a number of separate compressors with a common drive means and interconnected discharge and suction between stages. These prior art multistage compressors are frequently unsuitable for use where gases and vapors are to be withdrawn at intermediate pressures or are to be added in at intermediate pressures since the gas pumping capacity of each stage is changed thereby and, in consequence, some of the various pressures are also changed.
Herein the term compressor includes all of the several kinds of gas and vapor compressors, such as: piston and cylinder compressors; Roots type compressors; turbo compressors, etc. All compressors have a suction, or inlet, where the gas or vapor to be compressed enters the compressor, and a discharge, or outlet, where the compressed gas or vapor leaves the compressor. Herein the term compressor drive means includes all of the several means for driving compressors, such as: electric motors; steam turbines, gas turbines; internal combustion engines, etc.
It is a common, though not universal, practice to use a holding tank for each operating pressure of a compressor system. Where such holding tanks receive compressed gas or vapor from the compressor discharge, they are herein referred to as receivers. Where such holding tanks supply gas or vapor to the compressor suction, they are herein referred to as sources. In some cases, as for example intermediate pressure holding tanks for a multistage compressor, a single tank may function as a receiver and a source.